False statements or representation: Debt collection

I never entered into an agreement with this company. Nothing was sent to me to prove that entered into a contract with this company. I dont know who they are and I never agreed to do business with them. I can only suspect that someone hired them to collect a debt on another companies behalf. Which I have no communications with the original company explaining why I owe them money and they kept my security deposit.the house got sold to several companies while we rented it and the security deposit supposedly got lost in all the transitions